Process for bonding copper or iron to titanium or tantalum

ABSTRACT

COPPER OR IRON ARE SECURELY BONDED TO TITANIUM OR TANTALUM SUBSTRATE METAL BY INITIALLY SUBJECTING THE SUBSTRATE METAL TO IONIC BOMBARDMENT IN WHICH THE SUBSTRATE METAL PERFORMS THE ROLE OF A CATHODE AND THEN TO CATHODE SPUTTERING IN WHICH THE SUBSTRATE METAL PERFORMS THE ROLE OF AN ANODE, AND THE COPPER OR IRON THE ROLE OF A CATHODE. THEREAFTER, THE BONDED COPPER OR IRON IS SUPPLEMENTED BY ADDITIONAL DEPOSITS BY CONVENTIONAL MEANS SUCH AS ELECTRODEPOSITION, ETC. SUPERIOR INDUSTRIAL PRODUCTS RESULTING FROM THE PROCESS ARE USEFUL AS ANODES IN ELECTROLYSIS CELLS AND AS HEAT EXCHANGERS.

Sept. 10, 1974 RA EI'AL PROCESS FOR BONDING COPPER 0R 3,835,007 IRON T0TITANIUM on TANTALUM Filed D80. .13. 1972 United States Patent PROCESSFOR BONDING COPPER OR IRON TO TITANIUM OR TANTALUM Alain Ferat, RobertMasotti, and Hubert Chavanel, Lyon, France, assignors to Rhone-Progil,Paris, France Filed Dec. 13, 1972, Ser. No. 314,858 Claims priority,application France, Dec. 24, 1971, 7147874 Int. Cl. C23c /80 US. Cl.204-192 7 Claims ABSTRACT OF THE DISCLOSURE Copper or iron are securelybonded to titanium or tantalum substrate metal by initially subjectingthe substrate metal to ionic bombardment in which the substrate metalperforms the role of a cathode and then to cathode sputtering in whichthe substrate metal performs the role of an anode, and the copper oriron the role of a cathode. Thereafter, the bonded copper or iron issupplemented by additional deposits by conventional means such aselectrodepositiou, etc. Superior industrial products resulting from theprocess are useful as anodes in electrolysis cells and as heatexchangers.

BACKGROUND OF THE INVENTION The present invention relates to a newprocess of bond ing copper or iron to titanium or tantalum and to thenew industirial products resulting from it.

Bonding of these metals has been known for many years and has employedsuch processes as rolling, plating, hammering, co-drawing, classical orultra-sonic soldering. Those techniques are intended to permit one tobring together as closely as possible sheets or plates of titanium ortantalum and of another metal. This prior art bonding has also beenachieved by electro-deposition of a metal on a sheet or plate oftitanium 'or tantalum.

The results obtained by utilization of all those interestingconventional prior art methods are, however, often insufiicient for thecontemplated applications of the bonded product. Indeed, because of alack of homogeneity and adherence between the surfaces of the twometals, the bonding lacked tenacity and tear resistance between the twometals was relatively low.

The present invention contemplates, by using the process according toinvention, to provide an important solution of the problem of bondingtitanium or tantalum to copper or iron.

It is, accordingly, an object of the invention to provide a superiorbonding of copper or iron to titanium or tantalum.

It is another object of the present invention to provide an economicalmethod of tenaciously bonding these metals.

It is also an object of the invention to provide a superior bondedproduct of these metals.

Other objects of the invention will be apparent to those skilled in theart from the present description, taken in conjunction with the appendeddrawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. 1 'is a plan view of bonded sheets ofcopper (Cu) and titanium (Ti) in accordance with the invention, whichare employed to conduct a conductivity test, to be describedhereinbelow, showing one of the important advantages of the bondedproducts of the invention.

FIG. 2 is an elevation of the bonded sheets of FIG. 1.

GENERAL DESCRIPTION OF THE INVENTION In general the present inventioncomprises first depositing on titanium or tantalum, in accordance withcertain conditions, a thin adhering layer of the contemplated metal,copper or iron, the layer having a very strong adherence or bond withthe support metal, titanium or tantalum, then of increasing thisadhering layer by adding additional copper or iron by any known means.

To obtain a good adherence or bonding of the adhering metal layer on thesupport metal, it is necessary that the support metal surface isperfectly clean and in the free metal state, on which the adhering metallayer is deposited under conditions of the invention which avoid theformation of brittle compounds. Cathodic pulverization of copper or ironon the metal support, in accordance with the conditions of the inventionprovides a satisfactory bond- 'ing of the adhering layer of copper oriron.

The present process, consists of in a first stage, depositing a thinadhering layer of copper or iron on the support metal, then in a secondstage, adding by any known way additional amounts of deposited metallayer. This process is characterized in that the supporting metal(titanium or tantalum) is first subjected to a mechanical and/orchemical cleaning treatment, then to an ionic bombardment in a residualatmosphere of rare gas and receives afterwards a copper or iron depositby cathodic sputtering of one of these metals in a residual atmosphereof rare gas at a temperature of less than 500 C., the resulting adheringlayer of copper or iron being subsequently supplemented in any knownway.

It is necessary to employ a temperature less than 500 C. since in therange of 500 C. and upward, intermetal diffusion is no longer negligibleand leads to the compounds Ti (Me) or Ta (Me) which are highly brittle(Me being the deposited metal, x and y being integers). Cathodicsputtering of copper or iron on the support metal after ionicbombardment of the support metal, may be made on a cooled support metalas well as at high temperature resulting from the ionic bombardment.However, it is advantageous for the deposition of bonding metal to bemade in a temperature range of about 300 to 400 C. Under theseconditions, it is possible to deposit copper or iron bonding layer onthe support metal, which layer has a thickness of between about 0.5 and5 microns. This layer is then thickened or supplemented in any knownway, such as electro-deposition, etc. There is then obtained a finallayer having a thickness comprised between about 0.5 and 5 millimetersor more.

The techniques of cathodic sputtering are characterized by depositing ametal by electrical discharge in a low pressure of inert gas.

The apparatus for cathodic sputtering consists of a vacuum enclosure, apumping system, a high voltage electrical feed and an inert gasintroduction system.

The supporting metal (titanium or tantalum), before being introduced inthe vacuum enclosure is subjected to a thermal and/or chemical treatmentof sanding and/0r degreasing. This supporting metal and the metal to bepulverized are put in electrode position in enclosure containing a raregas residual atmosphere (such as argon). In the first stage of ionicbombardment the supporting metal is positioned cat'hodically in applyingnegative high voltage. It becomes the cathode for some time and a smallportion of the surface is pulverized. The other metal to be bonded isprotected during this operation, by means of a moving mask, againstbecoming contaminated with particles eminating from the support metal.This ionic bombardment of the support has for its purpose to degas andscour the surface which is to receive the deposit of other metal, byremoving oxide layers, traces of hydrocarbons, fats, etc. As a result,the surface of the support metal is converted as closely as possible tothe pure metallic state.

The supporting metal is next disconnected from the high voltage sourceand placedin the anode position ready to receive the deposit resultingfrom sputtering of the metal to be bonded (copper or iron), which isplaced in the cathode position. The copper or iron metal is cleared ofits mask and then connected to the high voltage source. Cathodesputtering on the anode is then conducted in a residual atmosphere ofpure rare gas, such as argon, radon, etc.

As a result of the foregoing conditions, the process of the inventionprovides a very strongly bonded layer or coating of copper or iron ontitanium or tantalum. Finally, after supplementing the bonded layer ofcopper or iron by conventional means, there is obtained a product whichhas mechanical and electrical characteristics high- 1y desirable for thecontemplated applications.

DETAILED DESCRIPTION OF THE INVENTION In order to disclose more clearlythe nature of the present invention, the following examples illustratingthe invention are given. It should be understood, however, that .this isdone solely by way of example and is intended neither to delineate thescope of the invention nor limit the ambit of the appended claims. Inthe examples which follow, and throughout the specification, thequantities of material are expressed in terms of parts by weight, unlessotherwise specified.

I. EXAMPLES OF BONDING COPPER TO TITANIUM(EXAMPLES 1-6) Although thenature and texture of the bonding produced by the present invention aredifiicult to define by the classical physico-chemical means, themechanical and electrical performances of the bonding resulting fromcathodic sputtering are readily ascertainable. Those characteristicswill be readily appreciated by comparison with the performances obtainedby depositions achieved by conventional means, such aselectro-deposition, shoopage, etc.

Example I A square titanium plate of 100 mm. on each side and 8/ mm.thick was scoured by subjecting it to a fluonitric attack by immersionfor 2 minutes in a mixture of nitric and hydrofluoric acids, washed withwater, then with acetone and finally dried.

Next are cleansed plate was introduced in a vacuum enclosure, thepressure of which was decreased to 10" torr. First, high voltage wasconnected to a copper target situated in front of the titanium plate andsubmitted in this way to a presputtering to remove copper surfaceimpurities which deposit on a moving mask placed between the coppertarget and titanium plate or support. Next, the titanium ionicbombardment phase was achieved by connecting the titanium plate to ahigh voltage source of continuous current of 3000 volts, under a partialpressure of pure argon, at approximately 40 10- torr. pressure for 30minutes. The titanium plate temperature was stabilized at the end ofthis operation at about 400 C. During all of the operation, the freshlycleaned copper target was protected by the moving mask. Next the highvoltage was connected to the copper target, and mask being removed,copper sputtering was made on the freshly scoured titanium, at atemperature near 350 C. This copper sputtering is made under theresidual atmosphere of pure argon of 20X 10- torr. pressure, at 3000volts, until obtaining a copper layer nearly 1 micron thick overportions of the titanium sheet (average deposit speed 300 angstroms perminute). The product obtained is illustrated by FIGS. 1 and 2 of thedrawings. The titanium plate with its very tenaciously adhering thincopper layer is removed from the enclosure after cooling for aboutminutes.

The thickness of the thin copper coating is increased byelectro-deposition of an additional copper layer of 1 mm. under thefollowing conditions: The work iece was introduced as the cathode intoan acid electrolysis bath of copper sulfate containing 250 grams perliter of cupric sulfate pentahydrate, 75 grams per liter of sulfuricacid (having a specific gravity of 1.66) in distilled Water. Theelectrolysis bath was stirred while at room temperature. The anode wasof copper. The density of the electrolysis current was 3 amperes persquare decimeter.

Example 2 Example 1 was repeated but the titanium plate was treated bysanding with Fontainebleau sand (40-80 microns) before the fluonitricattack.

Example 3 Example 1 was repeated, except that the copper deposition wasmade on a titanium plate freshly scoured and cooled for 30 minutes, at agreater speed, namely, 600 angstroms per minute.

Example 4 Example 1 was repeated, except that the titanium sheet wastreated by sanding before the fiuonitric attack and the copperdeposition was made on titanium while at room temperature at a speed of600 angstroms per minute.

Example 5 Example 1 was repeated, except that the titanium plate was notsubjected to any fluonitric attack.

Example 6 Example 1 was repeated, except that the titanium plate was notsubjected to fluoronitric attack, but instead to a sanding with corundumhaving a granule size of about 250 microns.

II. EXAMPLE OF BONDING IRON TO TITANIUM Example 7 Example 1 wasrepeated, but copper was replaced by iron in producing the iron bondingon the titanium sheet and the iron coating was then coated with a copperdeposit by electro-deposition under the following conditions. Theworkpiece was introduced as the cathode in an electrolysis bathcontaining 100 grams per liter of cupric sulfate pentahydrate, cc. perliter of diethylenetriamine and 10 cc. per liter of ammonium sulfate,all in distilled water. The deposition was conducted maintaining thebath at a temperature of about 60 C. with the electrolysis currentdensity being about 4 amperes per square decimeter. The anode was ofcopper.

III. EXAMPLE OF BONDING COPPER TO TANTALUM Example 8 Example 1 wasrepeated, except that the titanium plate was replaced by one of tantalumof the same dimensions.

IV. EXAMPLE OF BONDING IRON TO TANTALUM Example 9 Example 7 wasrepeated, except that the titanium plate was replaced by one of tantalumof the same dimensions.

Various tests were made to compare the qualities of the bondingresulting from utilization of the process of the invention with bondingsobtained with methods of the prior art.

ADHERENCE On the titanium sample sheet covered with a bonded copper oriron coating layer obtained by cathodic sputtering treatment of theseveral examples, surfaces of 2 mm. were delimited and protected with asilicone coating. The whole was then subjected to attack by nitric acidwhich dissolves copper or iron layer where it is not protected, by

silicone. Thus islets are obtained on titanium, presenting a copper oriron bonded layer which was then thickened with copper byelectro-deposition until a thickness was obtained which was sufficientfor achieving a tin brazing solder. After being brazed, a device wasobtained allowing one to measure the tear resistance under the influenceof a traction stress. Sheets of titanium bonded with copper by prior artmethods were also subjected to the same treat ment. The comparativeadhesion test results are shown in Table 1, below.

electro-deposition without any intermediary bonded layer 0.2 Copperlayer deposited directly on titanium by shoopage without anyintermediary bonded layer 0.2

MEASURE OF CONDUCTIVITY In a titanium sample covered with a copperbonded layer in accordance with the invention, thickened byelectro-deposi-tion of additional copper, a current of 0.5 ampere waspassed and the difference in potential between points about cm. apartwas measured.

The sample geometry was that shown in accordance with the appendeddrawings. The difference in potential was measured at various points; 3measures were made between points situated on titanium and copper, oncopper alone, and on titanium alone. The following results wereobtained, with a titanium thickness of 8/ 10 millimeter and a copperthickness of ll/ 10 millimeters:

Points position Difference in Potential Ti-Cu 0.85 X 10* volts Cu-Cu0.65 10- volts Ti-Ti 0.85 X 10- volts The results obtained on a titaniumplate of 8/10 millimeter without any copper deposition, was:

Ti-Ti 14.5 X 10 volts Calculating this value for 19/20 millimeters,which is the thickness of the plate covered with copper, the resultobtained is:

Ti-Ti 6.1 10- volts It is well known that electrical current is alwaysinclined to choose the path presenting the least resistance. Theinterpretation of results hereinabove permits one to determine that theelectrical current in a titanium sample, covered with copper bonding bythe process of the invention, is inclined to bypass copper through theachieved titanium-copper bonding, because the latter has a lowerresistance. Therefore, there is a very good electrical bonding betweentitanium and copper.

FOLDING AT 90 C.

Folding tests at 90 C. have shown that copper-titanium bonding achievedin accordance with the invention did not become detached. A notabledetachment is observed on a titanium sample covered directly with copperby electrodeposition without any intermediary bonded layer and on atitanium sample covered of copper by rolling.

The applications of the bonding process of the invention have shownthemselves to be especially interesting in the case of titanium andtantalum utilisation for their characteristics of corrosion resistance,the achieved bonding being obliged to have at least one of the followingproperties:

(1) Adherence homogeneity on the whole of the common surface, withoutbrittleness (2) Good electrical conductibility (application in anodesfor electrolysis) (3) Good thermal conductibility (applications in heatexchangers) The terms and expressions which have been employed are usedas terms of description and not of limitation, and there is no intentionin the use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof, but it isrecognized that various modifications are possible within the scope ofthe invention claimed.

What is claimed is:

1. A process of bonding a substrate metal selected from the classconsisting of titanium and tantalum with a coating metal selected fromthe class consisting of iron and copper, comprising, in a first stage,depositing a thin bond ing layer of coating metal on said substratemetal, and, in a second stage, of thickening the deposited layer in anyknown method with additional metal, characterized in that said substratemetal is first subjected to a preliminary cleaning treatment, then to anionic bombardment in a residual atmosphere of rare gas and afterwards abonded layer of said coating metal is deposited by cathodic sputteringon said substrate metal in residual atmosphere of rare gas at atemperature lower than 500 C, said bonded layer of said coating metalbeing thickened by addition of more metal.

2. A process according to Claim 1, wherein said cleaning treatmentconsists of a mechanical treatment.

3. A process according to Claim 1, wherein said cleaning treatment ofsaid substrate metal is a sanding with a material selected from theclass consisting of fine sand and corundum.

4. A process according to Claim 1, wherein said cleaning of saidsubstrate metal is made by scouring with a mixture of nitric andhydrofluoric acids.

5. A process according to Claim 1, wherein said substrate metal, aftercleaning treatment, is connected in a cathodic sputtering device, firstin the form of a target cathode, which sputters, under ionicbombardment, then in the form of an anode which receives a deposit ofcoating metal which is coupled as a cathode and which sputters.

6. A process according to Claim 1, wherein the thickness of the bondinglayer of coating metal deposited by cathodic sputtering is increased byelectrodeposition.

7. A process according to Claim 1, wherein said cleaning treatmentconsists of a chemical treatment.

References Cited UNITED STATES PATENTS 3,393,446 7/1968 Hughes et al204192 X 3,479,269 11/1969 Byrnes Jr. et al 204192 3,507,248 4/1970Seeley et al. 204298 X 3,649,503 3/1972 Terry 204192 3,723,276 3/1973Lane et al. 204192 JOHN H. MACK, Primary Examiner D. R. VALENTINE,Assistant Examiner

